Real Dictionary

Trojan horse
If you describe a person or thing as a Trojan horse, you mean that they are being used to hide someone's true purpose or intentions.

Trojan horse in American English
in the Trojan War, a huge, hollow wooden horse with Greek soldiers hidden inside that is left at the gates of Troy: the Trojans bring it into the city, thinking it a gift, and the soldiers creep out and open the gates to the rest of the Greek army, which
noun: a gigantic hollow wooden horse, left by the Greeks upon their pretended abandonment of the siege of Troy. The Trojans took it into Troy and Greek soldiers concealed in the horse opened the gates to the Greek army at night and conquered the city

Trojan Horse in British English
noun: the huge wooden hollow figure of a horse left outside Troy by the Greeks when they feigned retreat and dragged inside by the Trojans. The men concealed inside it opened the city to the final Greek assault